Bibliographic details of the publications referred to hereinafter in this specification are collected at the end of the description.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.
Type 2 diabetes results in chronic hyperglycaemia, hyperinsulinemia, insulin resistance, impaired insulin secretion and the risk of cardiovascular complications (1–4). A recent report (5) showed that there are more than 150 million people worldwide who suffer from diabetes mellitus, among which over 90% of the people have Type 2 diabetes. Currently, apart from insulin, no molecule of biological origin has been found useful for the treatment and management of Type 2 diabetes without further aggravating hyperinsulinemia which is believed to be a potential cause for the development of diabetes complications.
The isolation of a peptdic factor from human pituitary growth hormone extracts which accelerated glucose uptake in isolated rat hemi-diaphragms has been reported (6,7,8). The structure studies demonstrated that the molecule was a fragment of the amino terminal sequence of the growth hormone molecule. The amino-terminal region of human growth hormone (hGH) containing the amino acid sequence Leu-Ser-Arg-Leu-Phe-Asp-Asn-Ala (hGH 6–13) (SEQ ID NO:1) was found to enhance the actions of insulin in vitro and in vivo (9). This human growth hormone peptide was used for used for comparison in the course of the work on the urinary peptide factors.
Hypoglycaemic action of a semi-purified fraction of human urine has also been observed (10,11). This urinary fraction acted only in the presence of insulin in enhancing glucose uptake, glycogen synthesis, and glycogen synthetase conversion to the active form in vitro and in vivo. The similar in vitro or in vivo biological effects of this urinary fraction led to the assumption that it was the hGH (6–13) fragment of human growth hormone, although no unequivocal evidence was obtained to establish its identity. Studies with ultrafiltration, ion exchange and gel filtration chromatography indicated that the isolate from human urine was a peptidic compound (11).
In work leading to the present invention, the hypoglycaemic peptide in human urine has been isolated and purified, and its structure determined. In addition, this peptide has been chemically synthesised. The activity of both the isolated peptide and the chemically synthesised peptide have been examined in vitro and in vivo to demonstrate its insulin-potentiating effects by enhanced glucose uptake and glycogen synthesis in vitro and lowered blood glucose levels in vivo. In addition, peptide analogues of this isolated peptide have also been chemically synthesised, and certain of these analogues have also been shown to have significant biological effects on glucose metabolism both in vitro and in vivo.